NOVEL FUNCTIONAL 1D AND 2D CONJUGATED POLYMERS: DESIGN, SYNTHESIS AND CHARACTERIZATION LI HAIRONG NATIONAL UNIVERSITY OF SINGAPORE 2008 NOVEL FUNCTIONAL 1D AND 2D CONJUGATED POLYMERS: DESIGN, SYNTHESIS AND CHARACTERIZATION LI HAIRONG (M. Sc. Singapore-MIT Alliance, NUS, Singapore. B. Eng. Zhejiang University, PRC) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE 2008 NAME: LI HAIRONG DEGREE: DOCTOR OF PHILOSOPHY DEPARTMENT: CHEMISTRY THESIS TITLE: NOVEL FUNCTIONAL 1D AND 2D CONJUGATED POLYMERS: DESIGN, SYNTHESIS AND CHARACTERIZATION Abstract Design and characterization of novel conjugated polymers are of great importance in understanding the intrinsic properties to realize the practical applications in many aspects. Among the various conjugated polymers, poly(p-phenylene)s (PPPs) and its derivatives are of considerable interests due to their solvent tractability, high thermal and chemical stabilities, high quantum yield and versatile synthetic strategies. Our efforts focused on investigating the structure-property relations of rationally designed PPPs, seeking the potential sensor and biological applications of water soluble PPPs. Continuous endeavor to chemical modification of PPPs involved an introduction of conjugated side chain onto PPP backbone, with specific highlights of crystalline nature, aggregation phenomenon, unique photophysical and self-assembly properties arisen from extended conjugation and strong π-π interaction. Structure-property relations were further explored in cross-conjugated cruciform system and preliminary work was carried out on cross conjugated polyphenols for antioxidant and toxicity studies. Keywords: poly(p-phenylene), water soluble, biomineralization, cross-conjugated, sensor, photophysical properties, self-assembly, aggregation, crystal, cruciform, polyphenol, antioxidant, toxicity. ACKNOWLEDGEMENTS I am deeply grateful to a lot of people, who have supported this work by different means. Above all, I would like to express my sincere gratitude to my supervisor Prof. Suresh Valiyaveettil and co-supervisor Prof. Lim Chwee Teck for their constructive guidance, full support and constant encouragement. I sincerely thank all the current and former members of the group for their cordiality and friendship. I thank Akhila, Balaji, Colin, Elena, Hairyu, Gayathri, Jegadesan, Renu, Santosh, Sindhu, Sivamurugan, Shaowen, Sheeja, Shirley and Yean Nee for all the good times in the lab and helping exchange knowledge skills. I am grateful to Dr. Vetrichelvan for his sincere guidance and help in the beginning of my research. I also appreciate the assistance from Nurmawati in OM, TEM, SEM and Fathima in XRD, Nanofiber fabrication. Technical assistance provided by the staffs of the various laboratories at the Faculty of Science is gratefully acknowledged. I thank National University of Singapore Nanoscience and Nanotechnology Initiative for scholarship. Financial supports from Agency for Science and Technology Research and National University of Singapore are also acknowledged. Words cannot express my deepest gratitude to my beloved parents and grandparents. I wholeheartedly thank them for their understanding, moral support and encouragement. i TABLE OF CONTENTS Acknowledgments i Table of contents ii Summary vii Abbreviations and Symbols x List of Tables xiv List of Figures xvii List of Schemes xxiii Linear and Cross Conjugated Poly(pphenylenes) and Oligo(p-phenylenes)--Introduction 1.1 Conjugated polymers---What and Why? 1.2 Conjugated polymers---An overview 1.3 Poly(para-pheneylenes) (PPPs)---An important class of CPs 1.3.1 Overview of PPPs 1.3.2 Synthetic strategies of PPP and derivatives 1.3.3 Important photophysical properties---Brief introduction 10 1.3.3.1 Absorption and emission 10 Fluorescence lifetimes and quantum yields 12 Two photon absorption 14 1.3.3.2 1.3.3.3 1.3.4 Photophysical properties of typical PPPs 15 1.3.4.1 Linear PPPs 15 1.3.4.2 Cross conjugated macromolecules 33 ii 1.4 Scope and outline of the thesis 55 1.5 References 57 Synthesis and Comparison of StructureProperty Relationship of Symmetric and Asymmteric Water Soluble Poly (paraphenylenes) 68 2.1 Introduction 69 2.2 Experimental 70 2.3 2.2.1 Measurements 70 2.2.2 Synthesis 71 Results and discussion 75 2.3.1 Characterization of polymers 75 2.3.2. Thermal properties 76 2.3.3. Optical properties 76 2.3.4. Aggregation properties of polymers 78 2.3.5. Complexation studies 85 2.3.6. Packing structure in solid state 90 2.3.7. Polymer as template for controlled biomineralization mimics 92 2.4 Conclusion 97 2.5 References 97 iii Water Soluble Multifunctional Cross Conjugated Poly(para-phenylenes) as Stimuli Responsive Materials: Design, Synthesis, and Characterization 100 3.1 Introduction 101 3.2 Experimental 102 3.2.1 Measurements 102 3.2.2 Synthesis 103 3.3 Results and discussion 109 3.3.1. Characterization 109 3.3.2. Thermal properities 110 3.3.3. Absorption and emission spectra 111 3.3.4. Titration studies 112 3.3.5 Aggregation properties 122 3.3.6. Thin film and nanofiber 124 3.4 References 126 3.5 Conclusion 127 Synthesis and Structure-Property Investigation of Novel Poly(p-phenylenes) with Conjugated Side Chain 130 4.1 Introduction 131 4.2 Experimental 132 4.3 Synthesis 133 4.4 Results and discussion 138 iv 4.4.1 Characterization 138 4.4.2 Powder X-ray diffraction 139 4.4.3 Absorption and emission 140 4.4.4 Quantum yield and two photon absorption (TPA) 146 4.4.5. Time-correlated single-photon counting 147 4.4.6. Solid phase self-assembly and morphology 150 4.5 Conclusion 152 4.6 References 153 Synthesis and Characterization of Cross Conjugated Cruciforms with Varied Functional Groups 160 5.1 Introduction 161 5.2 Experimental 162 5.2.1 Synthesis 162 5.2.2 Characterization 165 5.3 Results and discussion 170 5.3.1. Thermal properties 170 5.3.2. Absorption and emission properties 170 5.3.3 X-ray diffraction studies 172 5.3.3.1 Powder XRD studies 172 5.3.3.2 Single crystal XRD studies 174 5.3.4 5.4 Liquid crystal study Conclusion 175 176 v 5.5 References 177 5.6 Appendix 179 Synthesis and Characterization of Cross Conjugated Polyphenols 185 6.1 Introduction 186 6.2 Experimental 188 6.3 Results and discussion 190 6.3.1 Synthesis 190 6.3.2 Characterization 200 6.3.3 Absorption and emission properties 201 6.3.4 Antioxidant properties 204 6.3.5 Bioactivity studies 207 6.4 Conclusion 213 6.5 References 213 Design, Synthesis and Characterization of Pyrene Derivatives with Conjugated Arms 216 7.1 Introduction 217 7.2 Synthesis and characterization 220 7.3 UV-Vis absorption and emission studies 224 6.4 Conclusion 229 6.5 References 229 List of publications 232 vi Summary Chapter is a literature review on history and recent development of conjugated macromolecules, with major efforts on linear poly(para-phenylenes) and cross-conjugated polymers and cruciforms. My research work started from the structure-property comparison of two sets of symmetrical and asymmetrical sulfonate water soluble poly(p-phenylenes) (PPPs) (Chapter 2). The polymers aggregated in water/tetrahydrofuran (THF) mixture through microphase separation of polar (water) and nonpolar (THF) groups into appropriate solvents and strong intermolecular interactions. The fluorescence of the polymers was quenched in the presence of analytes including viologen derivatives, cytochrome-C (Cyt-C) and metal ions in water with Stern-Volmer constant in order of 106 M-1, indicating the potential application in sensors. Light-emitting iso-oriented calcite crystals were synthesized by controlled crystallization in presence of the water soluble PPPs. The nature of the functional groups on the polymer backbone and their ordered pack played a crucial role for the selective morphogenesis of the crystals with controlled particle shape, size and orientation. The polymers in Chapter had only one acceptor, which limited their versatility. Therefore, further efforts were made towards water soluble cross-conjugated PPPs (Chapter 3). Polymers with two different acceptors and extended conjugation in twodimensions were able to respond to different kinds of analytes in trace amount via fluorescence quenching combined with a blue or red shift of UV-Vis absorption maximum vii Design, Synthesis and Characterization of Pyrene Derivatives with Conjugated Arms 7.1. Introduction Since the very first publication of efficient organic light emitting diodes (OLEDs) by Tang and co-workers in the late 1980s,1 the research into the development of organic materials as electroluminescent devices has been extensive. The widespread research into OLEDs is a result of the many advantages it possesses over the inorganic light emitting devices. The organic compounds are much more economical to synthesize and its processability into thin films are higher. The ease of its tunability to the desired emissive colour by structural modifications makes it more convenient in synthesis than the inorganic materials. Moreover, inorganic materials require the use of costly and complicated semiconductor technologies compared to the easier techniques such as coating methods.2 Amongst the different classes of materials, the polymers are generally of lower purity which affects their device lifetimes and efficiency. However, they are also the most promising candidates for fabrication of large full colour displays at economical rates. Small molecules, on the other hand, provide high purity and easy vacuum deposition condition that is favorable for their device efficiency. The main drawback is the limitation on size of the displays that can be accomplished. Oligomers, with molecular weight lying in the range of 1000-10,000g/mol, provides for the best of both worlds, as they incorporate properties intermediate of polymers and small molecules.3-5 Various aromatic compounds are used as core compounds. Pyrene is one potential candidate, pyrene is a tetracyclic aromatic hydrocarbon and belongs to the D2h point group.6 It has intense UV-Vis absorption in 240-310nm and emission at 360-380 nm. Due 217 Li Hairong National University of Singapore to the four fused aromatic rings, it is highly planar with strong π-delocalization energy.7 One main drawback of its planar structure is its tendency to form π-aggregates that would decrease its luminescence efficiency. However, it can be overcome by inclusion of attachments which disrupt the overall planarity of the molecule and hence decrease aggregation effects. It is known to be a good electron acceptor, thus is able to serve as a good electron transporter in OLEDs.8 10 Figure 7.1. Structure and ‘C’ atom labeling of pyrene. Bo-Cheng Wang et al.’s theoretical investigations on substitutions on pyrene revealed that the HOMO level is raised as an electron donating substituent is included. On the other hand, an electron acceptor attached lowers the LUMO of pyrene. They also noted that the combination of effects from both electron donating and electron withdrawing groups on pyrene results in an overall decrease in the energy gap between HOMO and LUMO. This decrease is greater than an inclusion of two electron withdrawing or electron donating groups on pyrene. It is also calculated that the greatest red shifts in absorption and emission wavelengths can be expected when the substituents are attached to positions 1,6 as compared to positions 2,7.7 Many different types of substituents have been attached to the pyrene core to enhance their use as optoelectronic devices. There are three main roles that the substituents play which are important to the overall structure of the designed target 218 Design, Synthesis and Characterization of Pyrene Derivatives with Conjugated Arms molecules. Firstly, of the utmost importance is the increase in π-conjugation of the parent core.9-15 This increase in conjugation will bring about the decrease in the HOMO-LUMO energy gap which could be used to fine-tune the desired emissive colour. Most common substituents used for this purpose are multiple bonds like acetylenes and double bonds. They provide for linear extension of conjugation that helps shift absorption and emission wavelengths. Phenyl rings are also adapted for the same role as it possesses a planar ring of π-electrons that are delocalized. Secondly, substituents can also change the distribution of the electron density on the parent core which helps fine-tune the HOMO-LUMO energy level.12-20 The addition of electron-withdrawing groups would decrease the energy levels of HOMO and LUMO but greater decrease is observed for LUMO. On the other hand, an electron-donating group increases the electron density of both orbitals but greater increases are observed on the HOMO. In both cases, they give rise to a decrease in the overall energy gap between HOMO and LUMO. Last but not least, substituents also help prevent the formation of aggregates.18-26 Phenyl rings not only extend πconjugation, but its bulky nature results in steric hindrance on the overall compound. Meanwhile, the long alkyl chains enable the material to be soluble in most organic solvents and hence more convenience is achieved during fabrication of the material as thin films. We are interested in synthesizing novel pyrene derivatives and investigating their photo-physical properties. These target molecules were designed to possess attachments which extend their conjugation and thus change the photo-physical properties. The photophysical properties by introducing different donor and acceptors onto pyrene core were investigated. 219 Li Hairong National University of Singapore 7.2. Synthesis and characterization (i) C8H17O C8H17O I (ii) Si(CH3)3 C8H17O I C8H17O C8H17O I (iv) (iii) I 5a I O2N I I O2N I C8H17O Br Br OC8H17 5b I (v) (vi) 6a I I Br Br 6b T1 C8H17O OC8H17 C8H17O OC8H17 NO2 Br (viii) (vii) 6a/6b Br O2N T2 OC8H17 C8H17O O2 N OC8H17 (ix) OC8H17 (xi) (x) O2N I T3 C8H17O C8H17O NO2 220 Design, Synthesis and Characterization of Pyrene Derivatives with Conjugated Arms Scheme 7.1. Synthetic routes of target compounds (T1-T3). (i) TMSA (2 eq.), 10 % Pd(OAc)2, 20 % PPh3, 20 % CuI, THF/Et3N, Yield: 85 %. (ii) K2CO3 (6 eq.), MeOH, Yield: 96 %. (iii) Tributylvinyltin (1.2 eq.), 10 % Pd(OAc)2, 20 % PPh3, 20 %CuI, THF/Et3N. Yield: 82 % (3), 70 % (4). (iv) I2 (1 eq.), KIO3 (0.4 eq.), 4mL H2SO4, CH3COOH/10 % H2O, 40 oC, Yield: 36.1 %, (v) Br2 (2 eq.), CCl4, 60oC, Yield: 59.3 % (overall). (vi) (6 eq.), 20 % Pd(OAc)2, 50 % PPh3, 40 % CuI, THF/Et3N. Yield: 45.3 %. (vii) (3 eq.), 20 % Pd(OAc)2, 50 % PPh3, 20 % CuI, THF/Et3N, Yield: 39.5 %. (viii) (3 eq.), 20 % Pd(OAc)2, 50 % PPh3, 40 % CuI, THF/Et3N, Yield: 46.3 %. (ix) TMSA (5 eq.), 20% Pd(OAc)2, 50% PPh3, 20% CuI, THF/Et3N, Yield: 48.1% (x) K2CO3 (6 eq.), MeOH, Yield: 45.7 %. (xi) 4-Nitro-1-iodobenzene (2.2 equiv), 20 % Pd(OAc)2, 50 % PPh3, 40 % CuI, THF/Et3N, Yield: 37.9%. Compounds (1),27 (2-(4-(2-ethylhexyloxyl-3,5-dimethylphenyl)ethynyl)trimethylsilane 5-ethynyl-1,3-dimethyl-2(2-ethylhexyloxy)benzene (2),27 1,3-dimethyl-2-(2- ethylhexyloxy)-5-vinylbenzene (3),28 1-nitro-4-vinylbenzene (4),29 Diiodopyrene (5a and 5b)30 and Dibromo-diiodopyrene (6a and 6b)30 were synthesized according to literatures. 1,6-dibromo-3,8-bis(2-(3,5-dimethyl-4-(octyloxy)phenyl)ethynyl)pyrene (7): 615 mg (1.01mmol) of mixture 6a and 6b was dissolved in a mixture of 30 mL freshly distilled THF and 20 mL of TEA. The mixture was stirred and purged in N2. After two hours, 45.1 mg (0.2 mmol, 20 % eq.) of palladium acetate, 76.6 mg (0.402 mmol, 40 % eq.) of CuI and 132 mg (0.503 mmol, 50 % eq.) of triphenylphosphine were added. After another hour of stirring, 1.3 g (5.03 mmol, eq.) of compound was added dropwisely into the reaction flask over a period of 30 mins. The reaction was kept overnight and performed under N2 atmosphere. The crude product was obtained by extraction with DCM and washed with saturated NH4Cl, brine and water. The purified compound was obtained using column chromatography using hexane/DCM as the eluen to afford a yellow liquid. Yield: 45%. 1H NMR (CDCl3, δ ppm): 8.41-8.59 (d, 2H, pyrene-H), 8.438.57 (d, 2H, pyrene-H), 8.35 (s, 1H, pyrene-H), 7.37 (s, 4H, Ar-H), 3.69-3.72 (d, 4H, OCH2), 2.34 (s, 12H, Ar-CH3), 0.84-1.77 (m, 30H, Alk-H). 13C NMR (CDCl3, δ ppm): 221 Li Hairong National University of Singapore 157.1, 156.6, 133.9, 133.2, 132.6, 131.1, 131.0, 130.0, 125.7, 123.1, 119.5, 118.0, 116.7 (Ar-C, Vinyl-C)), 96.8, 95.9 (ethynyl-C), 74.6 (OCH2), 40.7, 30.3, 29.6, 24.2, 23.6, 23.0, 14.0, 11.2 (Alk-C). Mass(EI): 872.5 (m/z). Elemental anaylsis: C: 71.56, H: 7.47; Found C: 71.73, H: 7.35. 1,6-diethynyl-3,8-bis(2-(3,5-dimethyl-4-(octyloxy)phenyl)ethynyl)pyrene (8): 760 mg (0.871 mmol) of compound was dissolved in a mixture of 30mL of freshly distilled THF and 20 mL of TEA. The mixture was stirred and purged in N2. After hours, 39 mg (0.174 mmol, 20 % eq.) of palladium acetate, 66.2 mg (0.348 mmol, 40 % eq.) of CuI and 113.9 mg (0.435 mmol, 50 % eq.) of triphenylphosphine were added. The reaction mixture was then heated to 70 oC. After 30 min, 1.20 mL of TMSA (0.23 mL, 10 eq.) was added dropwise over a period of 30 into the reaction mixture. The reaction mixture was kept stirring under N2 overnight at 70 oC. The crude product was obtained by extraction with DCM and washed with saturated NH4Cl and brine. The crude product was directly added into a two neck round bottom flask containing 45.6 mg of K2CO3 (0.331 mmol, 10 eq.) and 10 mL of MeOH. The reaction was left to stir under N2 and kept overnight. The purified compound was obtained using column chromatography using hexane/DCM as the eluent to afford yellow solid. Yield: 60%. 1H NMR (CDCl3, δ ppm): 8.63-8.74 (d, 2H, pyrene-H), 8.68-8.70 (d, 2H, pyrene-H), 8.36 (s, 2H, pyrene-H), 7.39 (s, 4H, phenyl H), 3.69-3.71 (d, 4H, OCH2), 3.64 (s, 2H, alkyne-H), 2.34 (s, 12H, Ar-CH3), 0.83-1.79 (m, 30H, Alk-H). 13C NMR (CDCl3, δ ppm): 156.9, 134.0, 132.2, 131.8, 131.4, 131.2, 130.5, 129.4, 126.9, 123.6, 119.7, 117.8 (Ar-C), 96.3, 93.1, 83.3, 81.7 (ethynyl-C), 74.8 (OCH2), 40.7, 31.5, 29.1, 23.7, 22.5, 16.2, 14.0, 11.2 (Alk-C). Mass (FAB): 762.3 (m/z). Elemental analysis: C: 88.15, H: 7.66; Found: C: 88.35, H: 7.49. 222 Design, Synthesis and Characterization of Pyrene Derivatives with Conjugated Arms 1,3,6,8-Tetrakis-{2-[4-(2-ethyl-hexyloxy)-phenyl]-vinyl}-pyrene (T1): A similar procedure was adopted for the synthesis of T1 as in the case of 8. Yield: 83 %. 1H NMR (CDCl3, δ ppm): 8.52 (s, 2H), 8.04 (d, J = 8.4 Hz, 4H), 7.63 (d, J = 7.5 Hz, 8H), 7.35 (d, J = 7.5 Hz, 8H), 6.98 (m, 8H), 3.92 (d, J = 5.5 Hz, 8H), 2.34 (s, 24H), 1.74 (m, 4H), 1.361.26 (m, 32H), 0.92 (m, 24H). 13 C NMR (CDCl3, δ ppm): 160.1, 132.5, 132.1, 131.0, 128.7, 128.5, 128.4, 127.8, 126.6, 124.4, 124.2, 124.1, 123.9, 123.5, 114.7 (Ar-C, vinylC), 71.3 (OCH2), 40.1, 31.2, 29.8, 24.6, 23.7 (Alk-C), 16.1 (CH3), 14.8, 11.8 (Alk-C). Mass (FAB): 1234.7 (m/z). Elemental analysis: C: 85.52, H: 9.30; Found: C: 85.97, H: 9.26. 1,6-Bis-[4-(2-ethyl-hexyloxy)-phenylethynyl]-3,8-bis-[2-(4-nitro-phenyl)-vinyl]pyrene (T2): A similar procedure was adopted for the synthesis of T2 as in the case of 8. Yield: 38 %. 1H NMR (CDCl3, δ ppm): 8.59 (d, J = 8.4 Hz, 2H), 8.42 (d, J = 8.4 Hz, 2H), 8.38 (s, 2H), 8.17 (d, J = 8.7 Hz, 4H), 7.53 (d, J = 8.4 Hz, 4H), 7.38 (s, 4H), 6.98 (m, 8H), 6.95 – 6.73 (m, 4H), 3.72 (d, J = 5.5 Hz, 4H), 1.74 (m, 2H), 1.36-1.26 (m, 16H), 0.92 (m, 12H). 13C NMR (CDCl3, δ ppm): 160.5, 144.5, 135.6, 131.0, 129.6, 129.0, 128.8, 127.8, 127.5, 126.5, 125.7, 124.9, 124.6, 124.2, 123.5, 123.4, 121.9, 119.2, 114.7 (Ar-C, vinylC), 93.4, 92.5 (ethynyl-C), 71.3 (OCH2), 40.1, 31.2, 29.8, 24.6, 23.7, 14.8, 11.8 (Alk-C). Mass (EI): 1008.5 (m/z). Elemental analysis: C: 80.92, H: 6.79; Found: C: 81.44, H: 6.76. 1,6-bis(2-(3,5-dimethyl-4-(octyloxy)phenyl)ethynyl)-3,8-bis(2-(4-nitrophenyl) ethynyl)pyrene (T3): A similar procedure was adopted for the synthesis of T3 as in the case of 8. Yield: 70 %. 1H NMR (CDCl3, δ ppm): 8.61 (d, 2H, pyrene-H), 8.44 (d, 2H, pyrene-H), 8.40 (d, 4H, Ar-H), 7.59 (d, 4H, Ar-H), 7.41 (s, 4H, Ar-H), 3.68-3.71 (d, 4H, 223 Li Hairong National University of Singapore OCH2), 2.34 (s, 12H, Ar-CH3), 0.83-1.79 (m, 30H). 13 C NMR (CDCl3, δ ppm): 156.9, 145.7, 133.9, 132.3, 131.7, 131.4, 129.2, 128.5, 126.8, 125.5, 123.7, 119.0, 118.5, 118.1 (Ar-C), 103.0, 101.2, 96.3, 89.6 (ethynyl-C), 71.4 (OCH2), 40.8, 30.4, 29.7, 23.7, 23.1, 16.3, 14.1, 11.2 (Alk-C). Mass (FAB): 1004.5 (m/z). Elemental analysis: C: 81.25, H: 6.42; Found: C: 81.67; H: 6.38. 7.3. UV-Vis absorption and emission studies Absorption and emission spectra for T1, T2, T3, pyrene and two precursors and were recorded in THF solution with a concentration of mg/mL. The results are shown in Figure 7.2 and summarized in Table 7.1. T0 T1 T2 T3 1.0 0.8 0.6 0.8 0.6 0.4 0.4 0.2 0.2 0.0 300 350 400 450 500 550 Wavelength (nm) 600 T0 T1 T2 T3 1.0 0.0 350 400 450 500 550 600 650 Wavelength (nm) Figure 7.2. UV-Vis absorption (left) and emission (right) of pyrene (T0), T1, T2, T3 and precursors and 8. 224 Design, Synthesis and Characterization of Pyrene Derivatives with Conjugated Arms Table 7.1. Summary of absorption and emission peak maxima and calculated band gap Compound Absorption (nm) Emission (nm) ΔE (eV) Pyrene (T0) 321 and 337 374, 385, 394 and 414 3.62 T1 366, 427, 457 and 484 508 2.40 T2 255, 336, 433 and 457 475, 504 2.58 T3 236, 257, 344, 433 and 488 521, 541 2.30 217, 317, 416, 437 460 and 479 2.84 254, 314, 327, 428 and 452 474 and 500 2.62 O1 394 467 3.14 O2 405 469 3.06 O3 388 447 3.19 O4 392 442 3.16 O5 399 454 3.10 O6 415 510 2.98 O7 426 509 2.91 O8 412 501 3.00 O9 414 488 2.99 O10 425 498 2.91 S X OC6H13 R= O1, O6 R O2, O7 R C6H13 C6H13 N C6H13 NO2 X = CH (O1-O5) X X=N (O6-O10) O3, O8 O4, O9 O5, O10 Figure 7.3. Molecular structures of cruciform O1-O10 reported in Chapter 5. 225 Li Hairong National University of Singapore From Figure 7.2 and Table 7.1, it is evident that the absorption and emission wavelengths for the three target molecules were red shifted compared to pyrene (T0) itself. Red shifts of 89-151nm in absorption maxima and 109-147nm in emission maxima were observed. The HOMO-LUMO energy gap decreased from 3.62 to 2.30-2.58 eV. To compare within the target molecules, T3 had the longest wavelength of absorption maxima and hence the lowest HOMO-LUMO energy gap. A close look at the fluorescence spectra of T2 and T3 showed that both compounds exhibited similar pattern, with one strong peak followed by a smaller peak. This could be due to their similar structures. The only difference in the structure lies in the spacers used. T2 has both alkyne and vinyl spacers while T3 has only alkyne spacers. As such, it is possible to draw a conclusion that alkyne provided better conjugation and showed a larger shift in emission maximum. Unlike T2 and T3, the emission spectrum of T1 is vastly different. The most probable explanation could be due to the structural differences. T1 is homo-substituted while T2 and T3 are substituted with both electron donating and electron withdrawing moieties. It is also evident that there is an increase of absorption and emission maxima, as well as a decrease in the HOMO-LUMO energy gap for T2 as compared with precursor 7. The absorption and emission maxima of were smaller than T2. This could be due to the presence of two bromide groups on the pyrene core which resulted in the decrease in electron density due to electron-withdrawing effect. With the addition of vinylbenzene moiety, the absorption maximum was increased by 20 nm while the emission increased by 24 nm. This 226 Design, Synthesis and Characterization of Pyrene Derivatives with Conjugated Arms increase was due to the extension of conjugation by the phenyl ring and the vinyl groups. The spectra of the two compounds were of similar pattern due to the similarity in structures. If we compare the absorption and emission among T3, and 8, it is evident that there is a gradual increase in both the absorption and emission maxima from 7, to T3. This was due to the increase in conjugation length from one molecule to another through structural modifications. It can be observed in the absorption spectra that the significant increase is in T3. This is due to the inclusion of two phenyl rings to the structure. The increase from to is not as great as the modification involves only an exchange of two bromide groups for two acetylene bonds. It was our interest to compare the photophysical properties of these pyrene derivatives with that of cross-conjugated oligomers in Chapter (molecular structures and absorption and emission maxima were recapped in Figure 7.3 and Table 7.1). It was obvious that pyrene derivatives had significantly lower band gap. The bandgap of O2 with alkoxy groups was 3.06 eV as compared with the value of 2.40 eV for T1 and 2.84 eV for compound 7. It was confirmed that the band gaps decrease in the order: benzene > naphthalene > anthracene > pyrene.31 This is mainly due to confinement effect. The variations of the frontier orbital energies and band gaps were correlated with the increase of both Coulomb and resonance integral; furthermore the confinement effect is associated with the conjugated system of the aromatic molecules. In other words, confining organic molecules in larger cavities was sufficient to alter their electronic properties as a consequence of the increase in the molecular orbital energies and decrease of the band gaps. O6 and O7 with donor-acceptor structures had bandgaps at 2.98 and 2.91 eV, 227 Li Hairong National University of Singapore respectively, which is higher than T2 (2.58 eV) and T3 (2.30 eV) with similar structure. The smaller bond twisted angle at pyerene compared to the OPP unit of O1-O10 (confirmed by single crystal studies of O5 in Chapter 5) permits the pyrene derivatives to deviate more from the rigid rod conformation and effectively adopt a coil like conformation. This particular conformation causes more π-stacking between the pyrene repeating units resulting in the red shift of the absorption maxima.32-33 Therefore the donor-accepter effect of pyrene derivatives might not be as significant as it seems. A good example is the comparison of T2 and compound 8, both have similar dimensions in conjugation but the former having extra acceptor group, yet the band gap difference was only 0.04 eV. In fact, both donor and acceptor segment should affect the overall conjugation but this is not additive. Close look at the structure of T1-T3 gives possible explanation that all segments linked to pyrene core is in meta-position relative to each other and delocalization of electrons is affected, which reduces the overall conjugation as compared to O1-O10 having ortho-connection. Therefore, there pyrene derivatives are not classified as cross-conjugated molecules by definition. More important positions are 1, 3, and as they are positions where the electron population of the HOMO level is localized (Figure 7.1).34 Hence, variations on these sites are crucial in manipulating the HOMO-LUMO energy gap.6 All in all, the photophysical properties of pyrene derivatives were restricted by no conjugation between arms while the cruciforms O1-O10 were restricted by highly twisted OPP segment affecting the effective conjugation. 228 Design, Synthesis and Characterization of Pyrene Derivatives with Conjugated Arms 7.4. Conclusion Pyrene derivatives T1, T2 and T3 were designed, synthesized and characterized. Absorption and emissions studies were investigated in detail. It was noted that all are blue-emitting compounds with absorption and emission wavelengths in the range of 426488 nm, and 508-541 nm, respectively. The HOMO-LUMO energy gap of the derivatives is in the range of 2.30-2.58 eV. A direct comparison with cross-conjugated cruciforms in Chapter was also given. 7.5. References 1. Tang, C. W.; VanSlyke, S. A. Appl. Phys. Lett. 1987, 51, 913. 2. Mitschke, U.; Bäüerle, P. J. Mater. Chem. 2000, 10, 1471. 3. Bolink, H. J.; Barea, E.; Costa, R. D.; Coronado, E.; Sudhakar, S.; Zhen, C.; Sellinger, A. Org. Elec. 2008, 9, 155. 4. Mitschke, U.; Bäüerle, P. J. Mater. Chem. 2000, 10, 1471. 5. Wu, K. C.; Ku, P. J.; Lin, C. S.; Shih, H. T.; Wu, F. I.; Huang, M. J.; Lin, J. J.; Chen, I. C.; Cheng, C. H. Adv. Funct. Mater., 2008, 18, 67. 6. Park, Y. H.; Lee, Y. H.; Park, G. Y.; Park, N. G.; Young, S. K.; Mol. 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Sagara, Y.; Mutai, T.; Yoshikawa, I.; Araki, K. J. Am. Chem. Soc. 2007, 129, 1520. 25. Kamikawa, Y.; Kato, T. Langmuir, 2007, 23, 274. 26. Tang, C.; Liu, F.; Xia, Y. J.; Lin, J.; Xie, L. H.; Zhong, G. Y.; Fan, Q. L.; Huang, W. Organic Electronics, 2006, 7, 155. 27. Chang, J. Y.; Y, J. R.; Shin, Y. S.; Han, M. J.; Hong, S. -K. Chem. Mater. 2000, 12, 1076. 28. Meier, H.; Holst, H. C. Adv. Synth. & Catal. 2003, 345, 1005. 29. Chretien, J. -M.; Mallinger, A.; Zammattio, F.; Le Grognec, E.; Paris, M.; Montavon, G.; Quintard, J. –P. Tetrahedron Lett. 2007, 48, 1781. 30. Xiao, J.; Xu, J.; Cui, S.; Liu, H.; Wang, S.; Li, Y. Org. Lett. 2008, 10, 645. 31. Zhang, L. Z.; Cheng, P. Phys. Chem. Comm. 2003, 6, 62. 32. Wilson, J. N.; Bunz, U. H. F. J. Am. Chem. Soc. 2005, 127, 4124. 33. Fratiloiu, S. Senthilkumar, K.; Grozema, F. C.; Christian-Pandya, H.; Niazimbetova, Z. I. ; Bhandari, Y. J. ; Galvin, M. E. ; Siebbeles, L. D. A. Chem. Mater. 2006, 18, 2118. 34. Phelan, N. F.; Orchin, M. J. Chem. Educ. 1968, 45, 633. 231 LIST OF PUBLICATIONS 1. Li, Hairong; Ng, D. C.; Asharani P. V. N.; Valiyaveettil, S. Synthesis and characterization of cross conjugated polyphenols. Submitted 2. Li, Hairong; Valiyaveettil, S. Synthesis and characterization of cross conjugated cruciforms with varied functional groups. Tetrahedron Lett. Submitted. 3. Nurmawati, M. H.; Ajikumar, P. K.; Heng, L.; Li, Hairong; Valiyaveettil, S. Crossconjugated poly(p-phenylene)-aided supramolecular self-organization of fullerene nanocrystallites. Chem. Commun. 2008, 4945 4. Li, Hairong; Manoj, P.; Nurmawati, M. H.; Xu, Q. H.; Valiyaveettil, S. Synthesis and structure-property investigation of novel poly(p-phenylenes) with conjugated side chains. Macromolecules 2008, 41, 8473. Poster presentation at International Conference on Materials for Advanced Technologies (ICMAT), Singapore, 2007. 5. Sindhu, S.; Jegadesan, S.; Li, Hairong; Ajikumar, P. K.; Vetrichelvan, M; Valiyaveettil, S. Synthesis and patterning of luminescent CaCO3-Poly(p-phenylene) hybrid materials and thin films. Adv. Func. Mater. 2007, 17, 1698. 6. Li, Hairong; Nurmawati M. H.; Valiyaveettil, S. Cross conjugated poly(pphenylenes) with strong π-π stacking force: synthesis and characterization. Polym. Mater. Sci. Eng. 2007, 97, 617. Poster presentation at 234th ACS National Meeting, Boston, USA. 7. Li, Hairong; Valiyaveettil, S. Water-soluble multifunctional cross-conjugated poly(p-phenylenes) as stimuli-responsive materials: design, synthesis, and characterization. Macromolecules 2007, 40, 6057. (Featured on the journal’s Most-Accessed Articles, 2007). 8. Li, Hairong; Valiyaveettil, S. Interesting sensory molecules based on cross conjugated water soluble poly(p-phenylenes). Polym. Mater. Sci. Eng. 2007, 96, 747. Oral presentation at 233rd ACS National Meeting, Chicago, USA. 9. Vetrichelvan, M.; Li, Hairong; Ravindranath, R.; Valiyaveettil, S. Synthesis and comparison of the structure-property relationships of symmetric and asymmetric water-soluble poly(para-phenylenes). J. Polym. Sci, Part A: Polym. Chem. 2006, 44, 3763. 10. Sindhu, S.; Jegadesan, S.; Li Hairong.; Valiyaveettil, S. Calcium rich biocomposites with tuned optical properties: a polymer driven approach. Polym. Prep. 2006, 47, 326. 11. Li, Hairong; Vetrichelvan, M.; Valiyaveettil, S. Synthesis of water soluble conjugated poly(p-phenylene)s for the biosensor applications. Polym. Prep. 2005, 46, 104. Poster presentation at 1st Nano-Engineering and Nano-Science Congress 2004, Singapore. 232 [...]... Singapore Chapter 1 Linear and Cross -conjugated Poly(p-phenylenes) and Oligo(pphenylenes) -Introduction 1 Linear and Cross -conjugated Poly(p-phenylene)s and Oligo(p-phenylene)s -Introduction 1.1 Conjugated polymers -What and Why? Conjugated polymers (CPs) are distinguished by semi-conducting or metallic organic macromolecules which consist of a backbone with alternating single and multiple bonds (Figure... poly(azomethine) and poly(oxadiazoles) etc., have been synthesized and well studied due to their interesting electroluminescence,18 photoinduced electron-transfer properties19 and its possibility for functionalization which has overcome 3 Linear and Cross -conjugated Poly(p-phenylene)s and Oligo(p-phenylene)s -Introduction the problems of intractability and insolubility Other attractive aspects such as flexible and. .. on structure of the polymers and quenchers All polymers were able to form smooth, flexible and uniform thin films with strong blue fluorescence Aligned nanofibers were also made successfully, thanks to the strong intermolecular electrostatic and π-π interactions These results provided a novel way to extend the capability in chemo- and bio-sensor applications It was found that the polymers in Chapter... cartoonistic representation of various pathways for electronic 101 xviii conjugations in 2D polymers, X and Y represent donor-acceptor type functional groups Figure 3.2 Molecular structures of target polymers 102 Figure 3.3 Normalized absorption (A) and emission (B) spectra of P1 (■), P2 (●), P3 (▲), P4 (□), P5 (○) and P6 (△) in water (20 mg/L) 111 Figure 3.4 Fluorescence spectra of P1 with titration... (A) The cancer cells without any polyphenol added, (B) control cells, IMR-90 without any polyphenol (C) and (D) 2c treated cancer cells and fibroblasts respectively; (E) and (F) represents 2d treated cancer cells and normal cells respectively (G) and (H) represents 2b treated cells cancer cells and normal cells respectively The % of cells is indicated with each histogram The cells are treated with... energy of the phenolic O-H bond and increasing the stability of resulting phenolate radicals In Chapter 7, pyrene derivatives with conjugated segment were reported, unlike the previous chapters, we’d like to extend the core size and investigate the effect of conjugation Absorption and emissions studies were performed and comparisons made amongst them and their precursors and the cruciforms reported in... Table 6.1 Absorption and emission maxima of 8b – e, 9b – e, 10b – e, 1b – e, 2b – e in THF (nm) 203 Table 6.2 TEAC values of the synthesized compounds and typical antioxidants 206 Chapter 7 Table 7.1 Summary of absorption and emission peak maxima and calculated band gap 225 xvi Figure No LIST OF FIGURES Page No Chapter 1 Figure 1.1 Chemical structures of some of the typical conjugated polymers 2 Figure... in exploring the synthesis of this simplest aromatic conjugated polymer with new and novel molecular architectures (Figure 1.2),28 simply due to the key advantages of PPPs arising from their conceptually simple and appealing molecular structure, high chemical stability compared with the classical polyacetylenes, and interesting physical properties However poor solubility of the unfunctionalized PPPs... not proceed as cleanly as desired and it is either incomplete or leads to chain fracture Moreover, there are only a small number of suitable precursor polymers available and it is imperative to develop new synthetic methods to circumvent such limitations 5 Linear and Cross -conjugated Poly(p-phenylene)s and Oligo(p-phenylene)s -Introduction Typical direct methods for PPP synthesis are: 1) oxidative condensation... bridges;47 4) PPPs 7 Linear and Cross -conjugated Poly(p-phenylene)s and Oligo(p-phenylene)s -Introduction with aza bridges.48 Based on these, variety of ladder and stepladder type PPPs were synthesized and maximize their potential as active materials in LEDs and polymer lasers R R R2 R1 R1 R2 R R R N Figure 1.3 Representative ladder-type PPP structures Traditionally, electrochemical synthesis of PPP was limited . THESIS TITLE: NOVEL FUNCTIONAL 1D AND 2D CONJUGATED POLYMERS: DESIGN, SYNTHESIS AND CHARACTERIZATION A A b b s s t t r r a a c c t t Design and characterization of novel conjugated polymers. NOVEL FUNCTIONAL 1D AND 2D CONJUGATED POLYMERS: DESIGN, SYNTHESIS AND CHARACTERIZATION LI HAIRONG NATIONAL UNIVERSITY OF SINGAPORE 2008 NOVEL FUNCTIONAL. NATIONAL UNIVERSITY OF SINGAPORE 2008 NOVEL FUNCTIONAL 1D AND 2D CONJUGATED POLYMERS: DESIGN, SYNTHESIS AND CHARACTERIZATION LI HAIRONG (M. Sc. Singapore-MIT Alliance,